Electron capture dissociation of complexes of diacylglycerophosphocholine and divalent metal ions: Competition between charge reduction and radical induced phospholipid fragmentation

Divalent metal complexes of phosphocholines, [Metal(II)(L)(n)](2+) (where Metal=Cu(2+), Co(2+), Mg(2+), and Ca(2+), L=1,2-dihexanoyl-sn-glycero-3-phosphocholine [6:0/6:0GPCho] and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine [16:0/18:1GPCho] and n=2-5), were formed upon electrospray ionization mass spectrometry (ESI/MS) of 8 mM solution of phosphocholine (L) with 4 mM metal salt (Metal). The electron capture dissociation (ECD) reactions of these [Metal(II)(L)(n)](2+) complexes were examined via Fourier-transform ion-cyclotron resonance mass spectrometry. A rich and complex chemistry was observed, including charge reduction and fragmentation involving losses of a methyl radical, trimethylamine, and the acyl chains. The predominant reaction channel was dependent on the size (n) of the complex, the metal and ligand used, and the size of the acyl chain. Thus charge reduction dominates the ECD spectra of the larger phosphocholine, 16:0/18:1GPCho, but is largely absent in the smaller 6:0/6:0GPCho. For complexes of 16:0/18:1GPCho, n=4-5, fragmentation from the head group mainly occurs via loss of the methyl radical and trimethylamine. At n=3, the relative abundance of fragments due to loss of acyl chain radicals increases. The abundances of ions arising from these radical losses increase further for the n=2 complexes, thereby providing information on the composition and position of the 16:0 and 18:1 acyl groups. Thus ECD of metal complexes provides structurally useful information on the phosphocholine, including the nature of the head group, the acyl chains, and the positions of the acyl chains.     

Size matters! Fragmentation chemistry of [Cu(L)n]2+ complexes of diacylglycerophosphocholines as a function of coordination number (n = 2-7)

[Cu(L)(n)](2+) complexes of 1,2-dihexanoyl-sn-glycero-3-phosphocholine (L = D6PC) are formed upon electrospray ionization mass spectrometry (ESI-MS) of an 8 mM solution of D6PC with 4 mM CuCl(2) in 10 mM ammonium acetate buffer, pH 6.1. The collision-induced dissociation (CID) reactions of the [Cu(L)(n)](2+) complexes were examined in a linear ion trap mass spectrometer. A rich fragmentation chemistry was observed, including: loss of a neutral ligand; intermolecular ligand-ligand S(N)2 methylation; metal ion induced ligand fragmentation via carboxylate abstraction; and phosphate abstraction. The dominant reaction channel depends on the size (n) of the complex. Thus loss of neutral ligand(s) is the sole reaction channel for n = 5-7. At n = 4, S(N)2 methylation and carboxylate abstraction start to compete with neutral ligand loss. At n = 2 the carboxylate abstraction and phosphate abstraction reactions dominate the CID spectrum. The carboxylate abstraction and phosphate abstraction reactions are likely to be driven via neighboring group pathways. PM3 calculations, carried out to compare competing neighboring pathways based on the relative stabilities of the product ions, suggest a preference for five-membered ring formation for ligand fragmentation involving both carboxylate and phosphate abstraction.     

Studies of polyfunctional O-ligands: Formation and stability of Mg(2+) and Ca(2+) complexes of 1,2,4,5-benzenetetracarboxylic acid in aqueous solution at 25 degrees

The stabilities of the Ca(2+) and Mg(2+) complexes with 1,2,4,5-benzenetetracarboxylic acid (pyromellitic acid) were studied potentiometrically, at 25 degrees . The species ML, MHL, MH(2)L, and M(2)L [L = pyromellitate(4-); M = Ca(2+), Mg(2+)] were found to be present in solution (for Mg(2+) the species MH(3)L was also found). The dependence of the formation constants on ionic strength, and the stability trends of the Ca(2+) and Mg(2+) complexes with carboxylate ligands, are discussed.     

Metal ion-binding properties of 1-methyl-4-aminobenzimidazole (=9-methyl-1,3-dideazaadenine) and 1,4-dimethylbenzimidazole (=6,9-dimethyl-1,3-dideazapurine). quantification of the steric effect of the 6-amino group on metal ion binding at the N7 site of the adenine residue

The stability constants of the 1:1 complexes formed between Mg(2+), Ca(2+), Sr(2+), Ba(2+), Mn(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), or Cd(2+) (=M(2+)) and 1-methyl-4-aminobenzimidazole (MABI) or 1,4-dimethylbenzimidazole (DMBI) were determined by potentiometric pH titrations in aqueous solution (25 degrees C; I = 0.5 M, NaNO(3)). Some of the stability constants were also measured by UV spectrophotometry. The acidity constants of the species H(2)(MABI)(2+) and H(DMBI)(+) were determined by the same methods, some twice. Comparison of the stability constants of the M(MABI)(2+) and M(DMBI)(2+) complexes with those calculated from log versus p straight-line plots, which were established previously for sterically unhindered benzimidazole-type ligands (=L), reveals that the stabilities of the M(MABI)(2+) and M(DMBI)(2+) complexes are significantly reduced due to steric effects of the C4 substituents on metal ion binding at N3. This effect is more pronounced in the M(DMBI)(2+) complexes. Considering the steric equivalence of methyl and (noncoordinating) amino groups (as they occur in adenines), it is concluded that the same extent of steric inhibition by the (C6)NH(2) group is to be expected on metal ion binding at N7 with adenine derivatives. The basicity of the amino group in MABI is significantly higher than in its corresponding adenine derivative. Indeed, it is concluded that in the M(MABI)(2+) complexes chelate formation involving the amino group occurs to some extent. The formation degrees of these "closed" species are calculated; they vary for the complexes of Mn(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), or Cd(2+) between about 50 and 90%. The stability of the M(MABI)(2+) and M(DMBI)(2+) complexes with the alkaline earth ions is very low but unaffected by the C4 substituent; this probably indicates that in these instances outersphere complexes (with a water molecule between N3 and the metal ion) are formed.     

Interactions of metal ions with monoaza crown ethers A15C5 and A18C6 carrying dansyl fluorophore as pendant in acetonitrile solution

The influence of metal cations Li(+), Na(+), K(+), Cs(+), Mg(2+), Ca(2+), Sr(2+), Ba(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Pb(2+) and Al(3+) on the spectroscopic properties of the dansyl (1-dimethylaminonaphthalene-5-sulfonyl) group covalently linked to monoaza crown ethers 1-aza-15-crown-5 (1,4,7,10,-tetraoxa-13-azacyclopentadecane) (A15C5) and 1-aza-crown-6 (1,4,7,10,13-pentaoxa-16-azacyclooctadecane) (A18C6) was investigated by means of absorption and emission spectrophotometry. Interaction of the alkali metal ions with both fluoroionophores is weak, while alkaline earth metal ions interact strongly causing 50 and 85% quenching of dansyl fluorescence of N-(5-dimethylamine-1-naphthalenesulfonylo)-1,4,7,10,-tetraoxa-13-azacyclopentadecane (A15C5-Dns) and N-(5-dimethylamine-1-naphthalenesulfonylo)-1,4,7,10,13-pentaoxa-16-azacyclooctadecane (A18C6-Dns), respectively. The Cu(2+), Pb(2+) and Al(3+) cations interact very strongly with dansyl chromophore, causing a major change in absorption spectrum of the chromophore and forming non-fluorescent complexes. The Co(2+), Ni(2+), Zn(2+), Mg(2+) cations interact moderately with both fluoroionophores causing quenching of dansyl fluorescence by several percent only.     

Ligand influence over the formation of dinuclear [2+2] versus trinuclear [3+3] Cu(I) Schiff base macrocyclic complexes

The preparation and characterization of three new macrocyclic ligands with pendant arms based on the [2+2] condensation of isophthalaldehyde and the corresponding triamine substituted at the central N-atom is reported. None of these new macrocyclic ligands undergo any equilibrium reaction, based on imine hydrolysis to generate [1+1] macrocyclic formation or higher oligomeric compounds, such as [3+3], [4+4], etc., at least within the time scale of days. This indicates the stability of the newly generated imine bond. In sharp contrast, the reaction of the [2+2] macrocyclic Schiff bases with Cu(I) generates the corresponding dinuclear Cu(I) complexes [Cu(2)(L(1))](2+), 1(2+); [Cu(2)(L(2))(CH(3)CN)(2)](2+), 2(2+); and [Cu(2)(L(3))(CH(3)CN)(2)](2+), 3(2+), together with their trinuclear Cu(I) homologues [Cu(3)(L(4))](3+), 4(3+); [Cu(3)(L(5))(CH(3)CN)(3)](3+), 5(3+); and [Cu(3)(L(6))(CH(3)CN)(3)](3+), 6(3+), where the [2+2] ligand has undergone an expansion to the corresponding [3+3] Schiff base that is denoted as L(4), L(5), or L(6). The conditions under which the dinuclear and trinuclear complexes are formed were analyzed in terms of solvent dependence and synthetic pathways. The new complexes are characterized in solution by NMR, UV-vis, and MS spectroscopy and in the solid state by X-ray diffraction analysis and IR spectroscopy. For the particular case of the L(2) ligand, MS spectroscopy is also used to monitor the metal assisted transformation where the dinuclear complex 2(2+) is transformed into the trinuclear complex 5(3+). The Cu(I) complexes described here, in general, react slowly (within the time scale of days) with molecular oxygen, except for the ones containing the phenolic ligands 2(2+) and 5(3+) that react a bit faster.     

Effect of metal ions (Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) and water coordination on the structure and properties of L-arginine and zwitterionic L-arginine

Interactions between metal ions and amino acids are common both in solution and in the gas phase. The effect of metal ions and water on the structure of L-arginine is examined. The effects of metal ions (Li(+), Na(+), K(+), Mg(2+), Ca(2+), Ni(2+), Cu(2+), and Zn(2+)) and water on structures of Arg x M(H2O)m , m = 0, 1 complexes have been determined theoretically by employing the density functional theories (DFT) and using extended basis sets. Of the three stable complexes investigated, the relative stability of the gas-phase complexes computed with DFT methods (with the exception of K(+) systems) suggests metallic complexes of the neutral L-arginine to be the most stable species. The calculations of monohydrated systems show that even one water molecule has a profound effect on the relative stability of individual complexes. Proton dissociation enthalpies and Gibbs energies of arginine in the presence of the metal cations Li(+), Na(+), K(+), Mg(2+), Ca(2+), Ni(2+), Cu(2+), and Zn(2+) were also computed. Its gas-phase acidity considerably increases upon chelation. Of the Lewis acids investigated, the strongest affinity to arginine is exhibited by the Cu(2+) cation. The computed Gibbs energies DeltaG(o) are negative, span a rather broad energy interval (from -150 to -1500 kJ/mol), and are appreciably lowered upon hydration.     

Comparison of the surprising metal-ion-binding properties of 5- and 6-uracilmethylphosphonate (5Umpa2- and 6Umpa2-) in aqueous solution and crystal structures of the dimethyl and di(isopropyl) esters of H2(6Umpa)

5- and 6-Uracilmethylphosphonate (5Umpa(2-) and 6Umpa(2-)) as acyclic nucleotide analogues are in the focus of anticancer and antiviral research. Connected metabolic reactions involve metal ions; therefore, we determined the stability constants of M(Umpa) complexes (M(2+)=Mg(2+), Ca(2+), Mn(2+), Co(2+), Cu(2+), Zn(2+), or Cd(2+)). However, the coordination chemistry of these Umpa species is also of interest in its own right, for example, the phosphonate-coordinated M(2+) interacts with (C4)O to form seven-membered chelates with 5Umpa(2-), thus leading to intramolecular equilibria between open (op) and closed (cl) isomers. No such interaction occurs with 6Umpa(2-). In both M(Umpa) series deprotonation of the uracil residue leads to the formation of M(Umpa-H)(-) complexes at higher pH values. Their stability was evaluated by taking into account the fact that the uracilate residue can bind metal ions to give M(2)(Umpa-H)(+) species. This has led to two further important insights: 1) In M(6Umpa-H)-cl the H(+) is released from (N1)H, giving rise to six-membered chelates (degrees of formation of ca. 90 to 99.9 % with Mn(2+), Co(2+), Cu(2+), Zn(2+), or Cd(2+)). 2) In M(5Umpa-H)$-cl the (N3)H is deprotonated, leading to a higher stability of the seven-membered chelates involving (C4)O (even Mg(2+) and Ca(2+) chelates are formed up to approximately 50 %). In both instances the M(Umpa-H)-op species led to the formation of M(2)(Umpa-H)(+) complexes that have one M(2+) at the phosphonate and one at the (N3)(-) (plus carbonyl) site; this proves that nucleotides can bind metal ions independently at the phosphate and the nucleobase residues. X-ray structural analyses of 6Umpa derivatives show that in diesters the phosphonate group is turned away from the uracil residue, whereas in H(2)(6Umpa) the orientation is such that upon deprotonation in aqueous solution a strong hydrogen bond is formed between (N1)H and PO(3) (2-); replacement of the hydro gen with M(2+) gives the M(6Umpa-H)-cl chelates mentioned.     

Binding modes in metal ion complexes of quinones and semiquinone radical anions: electron-transfer reactivity.

9,10-Phenanthrenequinone (PQ) and 1,10-phenanthroline-5,6-dione (PTQ) form 1:1 and 2:1 complexes with metal ions (M (n+)=Sc (3+), Y (3+), Mg (2+), and Ca (2+)) in acetonitrile (MeCN), respectively. The binding constants of PQ--M (n+) complexes vary depending on either the Lewis acidity or ion radius of metal ions. The one-electron reduced species (PTQ(-)) forms 1:1 complexes with M (n+), and PQ(-) also forms 1:1 complexes with Sc(3+), Mg(2+), and Ca(2+), whereas PQ(-) forms 1:2 complexes with Y(3+) and La(3+), as indicated by electron spin resonance (ESR) measurements. On the other hand, semiquinone radical anions (Q(-) and NQ(-)) derived from p-benzoquinone (Q) and 1,4-naphthoquinone (NQ) form Sc(3+)-bridged pi-dimer radical anion complexes, Q(-)--(Sc(3+))(n)--Q and NQ(-)--(Sc(3+))(n)-NQ (n=2 and 3), respectively. The one-electron reduction potentials of quinones (PQ, PTQ, and Q) are largely positively shifted in the presence of M (n+). The rate constant of electron transfer from CoTPP (TPP(2-)=dianion of tetraphenylporphyrin) to PQ increases with increasing the concentration of Sc(3+) to reach a constant value, when all PQ molecules form the 1:1 complex with Sc(3+). Rates of electron transfer from 10,10'-dimethyl-9,9'-biacridine [(AcrH)(2)] to PTQ are also accelerated significantly by the presence of Sc(3+), Y(3+), and Mg(2+), exhibiting a first-order dependence with respect to concentrations of metal ions. In contrast to the case of o-quinones, unusually high kinetic orders are observed for rates of Sc(3+)-promoted electron transfer from tris(2-phenylpyridine)iridium(III) [Ir(ppy)(3)] to p-quinones (Q): second-order dependence on concentration of Q, and second- and third-order dependence on concentration of Sc(3+) due to formation of highly ordered radical anion complexes, Q()--(Sc(3+))(n)--Q (n=2 and 3).     

Bis[1,1'-N,N'-(2-picolyl)aminomethyl]ferrocene as a redox sensor for transition metal ions

The compound bis[1,1'-N,N'-(2-picolyl)aminomethyl]ferrocene, L(1), was synthesized. The protonation constants of this ligand and the stability constants of its complexes with Ni(2+), Cu(2+), Zn(2+), Cd(2+) and Pb(2+) were determined in aqueous solution by potentiometric methods at 25 degrees C and at ionic strength 0.10 mol dm(-3) in KNO(3). The compound L(1) forms only 1:1 (M:L) complexes with Pb(2+) and Cd(2+) while with Ni(2+) and Cu(2+) species of 2 [ratio] 1 ratio were also found. The complexing behaviour of L(1) is regulated by the constraint imposed by the ferrocene in its backbone, leading to lower values of stability constants for complexes of the divalent first row transition metals when compared with related ligands. However, the differences in stability are smaller for the larger metal ions. The structure of the copper complex with L(1) was determined by single-crystal X-ray diffraction and shows that a species of 2:2 ratio is formed. The two copper centres display distorted octahedral geometries and are linked through the two L(1) bridges at a long distance of 8.781(10) Angstrom. The electrochemical behaviour of L(1) was studied in the presence of Ni(2+), Cu(2+), Zn(2+), Cd(2+) and Pb(2+), showing that upon complexation the ferrocene-ferrocenium half-wave potential shifts anodically in relation to that of the free ligand. The maximum electrochemical shift ([capital Delta]E(1/2)) of 268 mV was found in the presence of Pb(2+), followed by Cu(2+)(218 mV), Ni(2+)(152 mV), Zn(2+)(111 mV) and Cd(2+)(110 mV). Moreover, L(1) is able to electrochemically and selectively sense Cu(2+) in the presence of a large excess of the other transition metal cations studied.     

Evaluation of the metal binding properties of a histidine-rich fusogenic peptide by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) was used to investigate metal ion interactions of the 18 amino acid peptide fragment B18 (LGLLLRHLRHHSNLLANI), derived from the membrane-associated protein bindin. The peptide sequence B18 represents the minimal membrane-binding motif of bindin and resembles a putative fusion peptide. The histidine-rich peptide has been shown to self-associate into distinct supramolecular structures, depending on the presence of Zn(2+) and Cu(2+). We examined the binding of B18 to the metal ions Cu(2+), Zn(2+), Mg(2+), Ca(2+), Mn(2+) and La(3+). For Cu(2+), we compared the metal binding affinities of the wild-type B18 peptide with those of its mutants in which one, two or three histidine residues have been replaced by serines. Upon titration of B18 with Cu(2+) ions, we found sequential binding of two Cu(2+) ions with dissociation constants of approximately 34 and approximately 725 micro M. Mutants of B18, in which one histidine residue is replaced by serine, still exhibit sequential binding of two copper ions with affinities for the first Cu(2+) ion comparable to that of wild-type B18 peptide, but with a greatly reduced affinity for the second Cu(2+) ion in mutants H112S and H113S. For mutants in which two histidines are replaced by serines, the affinity for the first Cu(2+) ion is reduced approximately 3-10 times in comparison with B18. The mutant in which all three histidine residues are replaced by serines exhibits an approximately 14-fold lower binding for the first Cu(2+) ion compared with B18. For the other metal ions under investigation (Zn(2+), Mg(2+), Ca(2+), Mn(2+) and La(3+)), a modest affinity to B18 was detected binding to the peptide in a 1 : 1 stoichiometry. Our results show a high affinity of the wild-type fusogenic peptide B18 for Cu(2+) ions whereas the Zn(2+) affinity was found to be comparable to that of other di- and trivalent metal ions.     

Selective colorimetric and fluorometric sensing of Cu(II) by iminocoumarin derivative in aqueous buffer

A new iminocoumarin based receptor L (C(27)H(26)N(4)OS) is synthesized with pyridyl and benzothiazolyl functionality. Synthesis of L is easy and it is isolated in good yield. L shows a selective and distinct color change from yellow to orange with Cu(2+) over Li(+), Na(+), Ca(2+), Mg(2+), Cr(2+), Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Pb(2+), and Ag(+) whereas a slight change in color is also observed in the case of Hg(2+) but L shows selective fluorescent quenching only in the presence of Cu(2+) in aqueous HEPES buffer (pH 7.0). The naked eye detection limit of Cu(2+) is determined at 2 μM whereas an emission experiment shows a lower detection limit at 200 nM. Selectivity studies of L in presence of 50 equivalents of other ion(s) by emission experiment show no interference toward the detection of 1 equivalent of Cu(2+). Both UV-Vis and fluorescence studies in the presence of Cu(2+)-salts of different counter anions with various sizes and shapes (Cl(-), ClO(4)(-), NO(3)(-), CF(3)SO(3)(-), SO(4)(2-) and BF(4)(-)) show almost similar spectral output in buffer media irrespective of the nature of the counter anions. The detailed UV-Vis and fluorescence titration experiments suggest the existence of both 1:1 and 2:1 (L:Cu(2+)) complexation stoichiometry and EPR study shows d(x(2)-y(2)) ground state of the Cu(II) centre in the complex. Furthermore the formation of a mononuclear [Cu(L)(CH(3)CN)].2ClO(4) complex and the flexible conformation of L in the solid state are confirmed by the single-crystal X-ray structural study.     

Theoretical study of interaction of urate with li(+), na(+), k(+), be(2+), mg(2+), and ca(2+) metal cations

The geometries and energetics of complexes of Li(+), Na(+), K(+), Be(2+), Mg(2+), and Ca(2+)metal cations with different possible uric acid anions (urate) were studied. The complexes were optimized at the B3LYP level and the 6-311++G(d,p) basis set. Complexes of urate with Mg(2+), and Ca(2+)metal cations were also optimized at the MP2/6-31+G(d) level. Single point energy calculations were performed at the MP2/6-311++G(d,p) level. The interactions of the metal cations at different nucleophilic sites of various possible urate were considered. It was revealed that metal cations would interact with urate in a bi-coordinate manner. In the gas phase, the most preferred position for the interaction of Li(+), Na(+), and K(+) cations is between the N(3) and O(2) sites, while all divalent cations Be(2+), Mg(2+), and Ca(2+) prefer binding between the N(7) and O(6) sites of the corresponding urate. The influence of aqueous solvent on the relative stability of different complexes has been examined using the Tomasi's polarized continuum model. The basis set superposition error (BSSE) corrected interaction energy was also computed for complexes. The AIM theory has been applied to analyze the properties of the bond critical points (electron densities and their Laplacians) involved in the coordination between urate and the metal cations. It was revealed that aqueous solvation would have significant effect on the relative stability of complexes obtained by the interaction of urate with Mg(2+) and Ca(2+)cations. Consequently, several complexes were found to exist in the water solution. The effect of metal cations on different NH and CO stretching vibrational modes of uric acid has also been discussed.     

Stabilities and isomeric equilibria in aqueous solution of monomeric metal ion complexes of adenosine 5'-diphosphate (ADP3-) in comparison with those of adenosine 5'-monophosphate (AMP2-)

Under experimental conditions in which the self-association of the adenine phosphates (AP), that is, of adenosine 5'-monophosphate (AMP(2-)) and adenosine 5'-diphosphate (ADP(3-)), is negligible, potentiometric pH titrations were carried out to determine the stabilities of the M(H;AP) and M(AP) complexes where M(2+)=Mg(2+), Ca(2+), Sr(2+), Ba(2+), Mn(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), or Cd(2+) (25 degrees C; I=0.1 M, NaNO(3)). It is concluded that in the M(H;AMP)(+) species M(2+) is bound at the adenine moiety and in the M(H;ADP) complexes at the diphosphate unit; however, the proton resides in both types of monoprotonated complexes at the phosphate residue. The stabilities of nearly all the M(AMP) and M(ADP)(-) complexes are significantly larger than what is expected for a sole coordination of M(2+) to the phosphate residue. This increased complex stability is attributed, in agreement with previous (1)H NMR shift studies and further information existing in the literature, to the formation of macrochelates of the phosphate-coordinated metal ions with N7 of the adenine residues. On the basis of recent measurements with simple phosphate monoesters and phosphonate ligands (R-MP(2-)) as well as with diphosphate monoesters (R-DP(3-)), where R is a noncoordinating and noninhibiting residue, the increased stabilities of the M(AMP) and M(ADP)(-) complexes due to the M(2+)-N7 interaction could be evaluated and the extent of macrochelate formation calculated. The results show that the formation degrees of the macrochelates for the complexes of the alkaline earth ions are small (about 15 % at the most), whereas for the 3d metal ions as well as for Zn(2+) and Cd(2+) the formation degrees vary between about 15 % (Mn(2+)) and 75 % (Ni(2+)) with values of about 40 and 50 % for Zn(2+) and Cu(2+), respectively. It is interesting to note, taking earlier results for M(ATP)(2-) complexes also into account (ATP(4-)=adenosine 5'-triphosphate), that for a given metal ion in nearly all instances the formation degrees of the macrochelates are within the error limits the same for M(AMP), M(ADP)(-) and M(ATP)(2-) complexes; except for Co(2+) and Ni(2+) it holds M(AMP) > M(ADP)(-) approximately M(ATP)(2-). This result is astonishing if one considers that the absolute stability constants of these complexes, which are determined largely by the affinity of the phosphate residues, can differ by more than two orders of magnitude. The impact and conclusions of these observations for biological systems are shortly lined out.     

Synthesis and solution studies of the complexes of trivalent lanthanides with the tetraazamacrocycle TETA-(PO)(2)

A new potentially multidentate hexaprotic ligand H(6)[TETA-(PO)(2)] has been prepared by reaction of ethylenediamine-N,N'-diacetic acid (EDDA), paraformaldehyde, and phosphinic acid; its coordination properties with three lanthanide ions (La(3+), Gd(3+), and Lu(3+)) have been explored. The structures of the complexes were studied in aqueous solution by potentiometric pH titrations and by (31)P NMR spectroscopy. Four acidity constants were determined potentiometrically in the range 2.5 < pH < 14. The four measured pK(a) values can be divided into two groups, and within each group the initial deprotonation was found to have little effect on the second. Variable temperature (31)P and (31)P[(1)H] EXSY NMR spectra showed that, for [Lu(TETA-(PO)(2))](3-), the two phosphorus atoms exist in different chemical environments and undergo an exchange process which is very fast on the NMR time scale at room temperature. This result is consistent with one of the phosphinate residues coordinating the metal ion and exchanging with a free analogue. In the case of [La(TETA-(PO)(2))](3-), only one temperature invariant signal is observed in (31)P NMR spectra; it corresponds to both phosphinate residues remaining uncoordinated to La(3+). The stability of [Ln(TETA-(PO)(2))](3-) has an order of La(3+) > Gd(3+) > Lu(3+). The coordination of one phosphinate residue to Lu(3+) brings the metal ion closer to the plane of four nitrogens and farther from the four carboxylate arms, resulting in [Lu(TETA-(PO)(2))](3-) having a lower stability than the corresponding La(3+) and Gd(3+) complexes. A pM-pH distribution diagram showed that introducing two phosphinate groups into TETA renders [Gd(TETA-(PO)(2))](3-) more stable than [Gd(TETA)](-). The selectivity factor of the ligand for Gd(3+) vs Ca(2+), Zn(2+), and Cu(2+) has been calculated, and the hydration number for [Dy(TETA-(PO)(2))](3-) has been measured by (17)O NMR spectroscopy to be zero.     

A convenient method for the preparation of barbituric and thiobarbituric acid transition metal complexes

A convenient method for the preparation of barbiturate transition metal complexes: (i) Cr(3+), Mn(2+), Fe(3+), Zn(2+) and Cd(2+) ions with barbituric acid (H(2)L) and (ii) Cr(3+) and Mo(5+) with 2-thiobarbituric acid (H(2)L') was reported and this has enabled seven complexes to be formulated as: [Cr(HL)(2)(OH)(H(2)O)].H(2)O, [Mn(HL)(2)(H(2)O)(2)], [Fe(2)(L)(OH)(3)(H(2)O)(4)].2H(2)O, [Zn(HL)(2)], [Cd(HL)(2)], [Cr(HL')(OH)(2)(H(2)O)].H(2)O and [Mo(HL')(2)]Cl. These new barbiturate complexes were synthesized and characterized by elemental analysis, molar conductivity, magnetic measurements, spectral methods (mid infrared, (1)H NMR, mass, X-ray powder diffraction and UV/vis spectra) and simultaneous thermal analysis (TG and DTG) techniques. The molar conductance measurements proved that, all complexes of barbituric and 2-thiobarbituric acids are non-electrolytes except for [Mo(HL')(2)]Cl. The electronic spectra and magnetic susceptibility measurements were used to infer the structures. The IR spectra of the ligands and their complexes are used to identify the mode of coordination. Kinetic and thermodynamic parameters such as: E, DeltaH, DeltaS and DeltaG are estimated according to the DTG curves. The two ligands and their complexes have been studied for their possible biological antifungal activity.     

Synthesis and photopysical properties of a polioxo ethylene chain alkaline earth metal fluorescent sensor with 2-aminoanthracene as terminal group

A new symmetric polioxo ethylene chain fluorescent probe containing 2-aminoanthracene bichromophoric as the terminal group for the alkaline earth metal cation, 2,2'-[oxybis(3-oxapentamethyleneoxy)]-bis[N-(2-anthryl)benzamide)] (1), has been synthesized. The photophysical properties of 1 have been studied by means of absorption, fluorescence spectroscopy, and (1)H NMR. The difference in emission spectra response to concentration of model compound 2-acetamido-anthracene and 1 in acetonitrile implies that intermolecular excited dimers is likely to occur. Fluorescence decay profiles of 2-acetamido-anthracene can be described by a biexponential fit, while three lifetimes, two of which are similar as those of 2-acetamido-anthracene, are found for 1. The third lifetime might be attributed to intramolecular excited dimers. Complex formation with alkaline earth metal ions are investigated in acetonitrile as solvent via fluorimetric titrations. Fluorescence intensity trend of the complex with Mg(2+) differed from those of other alkaline earth metal ions. The compound forms 1:2 (ligand/Mg(2+)) complex with Mg(2+) while formed 1:1 complexes with Ca(2+), Sr(2+), and Ba(2+), producing large hypochromic shifts in the emission spectra and significant cation-induced fluorescence amplifications. On the contrary, the addition of Ca(2+), Sr(2+), or Ba(2+) lead to a decrease in the fluorescence emission first, then an increase and blue shift in emission could be found at the end.     

Lanthanide(III) and group 13 metal ion complexes of tripodal amino phosphinate ligands

The tripodal amino-phosphinate ligands, tris(4-(phenylphosphinato)-3-benzyl-3-azabutyl)amine (H(3)ppba.2HCl.H(2)O) and tris(4-(phenylphosphinato)-3-azabutyl)amine (H(3)ppa.HCl.H(2)O) were synthesized and reacted with Al(3+), Ga(3+), In(3+) and the lanthanides (Ln(3+)). At 2 : 1 H(3)ppba to metal ratios, complexes of the type [M(H(3)ppba)(2)](3+)(M = Al(3+), Ga(3+), In(3+), Ho(3+)-Lu(3+)) were isolated. The bicapped [Ga(H(3)ppba)(2)](NO(3))(2)Cl.3CH(3)OH was structurally characterized and was shown indirectly by various techniques to be isostructural with the other [M(H(3)ppba)(2)](3+) complexes. Also, at 2 : 1 H(3)ppba to metal ratios, complexes of the type [M(H(4)ppba)(2)](5+)(M = La(3+)-Tb(3+)) were characterized, and the X-ray structure of [Gd(H(4)ppba)(2)](NO(3))(4)Cl.3CH(3)OH was determined. At 1 : 1 H(3)ppba to metal ratios, complexes of the type [M(H(4)ppba)](4+)(M = La(3+)-Er(3+)) were isolated and characterized. Elemental analysis and spectroscopic evidence supported the formation of a 1 : 1 monocapped complex. Reaction of 1 : 1 ratios of H(3)ppa with Ln(3+) and In(3+) yielded complexes of the type [M(H(3)ppa)](3+)(M = La(3+)-Yb(3+)) but with Ga(3+), complex of the type [Ga(ppa)].3H(2)O was obtained. Reaction of 1 : 1 ratios of H(3)ppa with Ln(3+) and In(3+) yielded complexes of the type [M(H(3)ppa)](3+)(M = La(3+)-Yb(3+)) but with Ga(3+) a neutral complex [Ga(ppa)].3H(2)O was obtained. The formation of an encapsulated 1 : 1 complex is supported by elemental analysis and spectroscopic evidence.     

Synthesis and Properties of 5-Chloro-8-hydroxyquinoline-Substituted Azacrown Ethers: A New Family of Highly Metal Ion-Selective Lariat Ethers

New 5-chloro-8-hydroxyquinoline (CHQ)-substituted aza-18-crown-6 (4), diaza-18-crown-6 (1), diaza-21-crown-7 (2), and diaza-24-crown-8 (3) ligands, where CHQ was attached through the 7-position, and aza-18-crown-6 (11) and diaza-18-crown-6 (10) macrocycles, where CHQ was attached through the 2-position, were prepared. Thermodynamic quantities for complexation of these CHQ-substituted macrocycles with alkali, alkaline earth, and transition metal ions were determined in absolute methanol at 25.0 degrees C by calorimetric titration. Two isomers, 1 and 10, which are different only in the attachment positions of the CHQ to the parent macroring, exhibit remarkable differences in their affinities toward the metal ions. Compound 1 forms very stable complexes with Mg(2+), Ca(2+), Cu(2+), and Ni(2+) (log K = 6.82, 5.31, 10.1, and 11.4, respectively), but not with the alkali metal ions. Ligand 10 displays strong complexation with K(+) and Ba(2+) (log K = 6.61 and 12.2, respectively) but not with Mg(2+) or Cu(2+). The new macrocycles and their complexes have been characterized by means of UV-visible and (1)H NMR spectra and X-ray crystallography. New peaks in the UV spectrum of the Mg(2+)-1 complex could allow an analytical determination of Mg(2+) in very dilute solutions in the presence of other alkali and alkaline earth metal cations. (1)H NMR spectral and X-ray crystallographic studies indicate that ligand 10 forms a cryptate-like structure when coordinated with K(+) and Ba(2+), which induces an efficient overlap of the two hydroxyquinoline rings. Such overlapping forms a pseudo second macroring that results in a significant increase in both complex stability and cation selectivity.